Conventionally, various vehicle seat reclining apparatuses are known for inclining a seatback relative to a seat cushion. These vehicle seat reclining apparatuses adjust and hold the seatback at an optimal inclination that is suitable for an occupant to be seated.
One of the known vehicle seat reclining apparatus is disclosed in JP2000-245561A (see FIG. 3). According to this vehicle seat reclining apparatus, when a large external force because of a vehicle impact, or the like, is applied in a rotational direction in which the seatback is inclined, a holding strength of the inclination is increased. More particularly, a first member of the vehicle seat reclining apparatus is provided with a substantially recess formed inner gear, and a second member of the vehicle seat reclining apparatus is provided with a guide wall. By operating (forward and backward) a locking member having outer teeth, with which the inner gear is meshed, in such a manner that the locking member is guided in the radial direction by means of the guide wall, the vehicle seat reclining apparatus changes lock/unlock condition (hold/release of the inclination) of the first and second members.
The vehicle seat reclining apparatus further includes an over-locking member for an emergency. The over-locking member is normally separated from the inner gear in the radial direction, and thus teeth of the over-locking member do not mesh with the inner gear. However, in a locked condition of the first and second members, when a large external force in the rotational direction is applied, the guide wall is pressed in a circumferential direction by means of the locking member and deformed. On this occasion, because of a deformation of the guide wall, the over-locking member is pressed outwardly in the radial direction, and the teeth of the over-locking member are thereby meshed with the inner gear. Accordingly, a locking strength of the first and second members of the vehicle seat reclining apparatus is increased and the holding strength of the inclination is thereby increased.
However, the vehicle seat reclining apparatus disclosed in JP2000-245561A includes at least, besides the locking members for normal lock/unlock operations (hold/release of the inclination), the over-locking member for an emergency. Therefore, the number of components is increased, and thus a manufacturing cost of the vehicle seat reclining apparatus being expensive.
A need thus exists for a vehicle seat reclining apparatus, which, without increasing the number of components, increases the holding strength in a condition where a large external force in the rotational direction is applied.